Silver halide emulsion

Abstract

A silver halide emulsion comprising at least a dispersion medium and silver halide grains is disclosed, wherein the silver halide grains comprise tabular grains having, as the main planes, {100} planes and having an aspect ratio (diameter/thickness) of 1.5 or more, in a proportion of 10% or more of the sum of the projected areas of all the grains, and the tabular grains each has at least one discontinuous halogen composition gap plane in their central part in such a way that the gap involves at least a difference of from 10 to 100 mol % in terms of the Cl - content or the Br - content or a difference of from 5 to 100 mol % in terms of the I - content between the adjacent layers. The reproducibility of the emulsion is good. The emulsion has high sensitivity, good graininess and good ability of forming high-quality photographic images.

What is claimed is: 
     
       1. A silver halide emulsion comprising at least a dispersion medium and silver halide tabular grains, wherein said silver halide tabular grains are prepared at least by a seed grain formation step followed by a ripening step and then a grain growth step, wherein the silver halide tabular grains having, as the main planes, {100} planes and having an aspect ratio (diameter/thickness) of 1.5 or more and are present in a proportion of 30% or more of the sum of the projected areas of all the silver halide tabular grains, wherein the seed grains, which during said grain growth step are grown to become said silver halide tabular grains, are formed during said seed grain formation step and said seed grains contain at least one halogen composition gap plane, and one of said at least one halogen composition gap plane is expressed by AgX 1  /AgX 2 , which is formed by laminating an AgX 2  layer on an AgX 1  nucleus, and the halide content X 1  differs from the halide content X 2  by at least 10 mol % in terms of Br -  content. 
     
     
       2. The silver halide emulsion as claimed in claim 1, wherein the tabular silver halide grains have a Cl -   content of 49 mol % or less. 
     
     
       3. The silver halide emulsion as claimed in claim 1, wherein said tabular grains further comprise a second halogen composition gap plane in said seed grains, wherein the halide content X 1  differs from the halide content X 2  by at least 10 mol % in terms of Cl -   or Br -  content or at least 5 mol % in terms of I -   content. 
     
     
       4. The silver halide emulsion as claimed in claim 1, wherein the difference between X 1  and X 2  is from 30 to 100 mol % in terms of the Br -   content. 
     
     
       5. The silver halide emulsion as claimed in claim 1, wherein said tabular grains have an aspect ratio of from 3 to 25. 
     
     
       6. The silver halide emulsion as claimed in claim 1, wherein said tabular grains constitute from 60 to 100% of all of the silver halide grains in the emulsion, based on projected area of all of the silver halide grains. 
     
     
       7. The silver halide emulsion as claimed in claim 1, wherein said tabular grains have a thickness in the range of from 0.03 to 0.3 μm. 
     
     
       8. The silver halide emulsion as claimed in claim 1, wherein said tabular grains exhibit a variation coefficient of grain size distribution of from 0 to 0.4. 
     
     
       9. The silver halide emulsion as claimed in claim 1, wherein said seed grains have an equivalent diameter, which corresponds to the diameter of a circle having the same area as the projected area of the seed grains, of 0.3 μm or less. 
     
     
       10. The silver halide emulsion as claimed in claim 1, wherein said ripening step was conducted at a temperature that is at least 10° C. higher than the seed grain formation step temperature. 
     
     
       11. The silver halide emulsion as claimed in claim 1, wherein the halogen composition gap plane AgX 1  /AgX 2  is formed by the following steps: a) AgX 1  seed grains are formed,   b) thereafter an X -   salt solution is added thereto, causing halogen conversion of the AgX 1 , wherein the X -   salt has a halide composition that forms a less soluble silver halide salt than the AgX 1 .